1. Field
Embodiments relate to a touch screen to smooth a moving trajectory of a touch unit input as a curved line and to display the moving trajectory and a display method of the touch screen.
2. Description of the Related Art
Technology for expressing letters on a touch screen or a touch pad, which is a digital medium, using a touch unit, such as a pen, like writing letters on paper, which is an analog medium, using a pen, has been developed. A digital handwritten letter includes at least one handwritten stroke. When a user moves a touch unit while the touch unit is in contact with a touch screen, a handwritten stroke is created. The handwritten stroke may include (x, y) coordinates corresponding to the end position of the touch unit.
For example, a user may move a touch unit on a touch screen of a computer system to write a letter. At this time, the computer system may sample (x, y) coordinates along a trajectory of the end position of the touch unit and display sampled coordinates. The sampled coordinates indicate points on the created moving trajectory of the touch unit. Sampled data from the touch screen include discrete time-series points.
Conventional methods of interpolating such sampled points include post-processing smoothing and simultaneous line-interpolation.
In the post-processing smoothing, a computer system sequentially stores sampled points in a memory while a user moves a touch unit on a touch screen, connects the points to create straight lines, and displays the straight lines. When the user separates the touch unit from the touch screen, all of the sampled points stored in the system are processed using spline interpolation to create a smooth curve, and the smooth curve is stored in the memory. Subsequently, the screen is cleared, and the created curve is displayed on the screen.
In the simultaneous line-interpolation, a computer system creates sampled coordinates of a touch unit as circles corresponding to pressure in a memory whenever the sampled coordinates and pressure of the touch unit are input while a user moves the touch unit on a touch screen, connects the points to create straight lines, creates quadrangles constituted by tangent lines between an old sampled circle and a new sampled circle in the memory (FIG. 1), and displays the circles and the quadrangles (FIG. 2).
In the post-processing smoothing, however, the sampled points are connected as straight lines while the user moves the touch unit on the touch screen, with the result that strokes connected in smoothed curves, similar to handwriting, are not displayed on the screen. Furthermore, the sampled points are interpolated in a straight line with a fixed width, with the result that the width of the moving trajectory of the touch unit is not smoothly changeable in correspondence to external factors such as pressure. For example, broken lines may occur.
In addition, a trajectory of the touch unit drawn after the user separates the touch unit from the touch screen may be different from the former trajectory of the touch unit. An image displayed on the screen while the touch unit moves on the touch screen is different from an image created after the touch unit is separated from the touch screen, with the result that the user may not accurately be aware of a final trajectory during movement of the touch unit. Also, whenever the moving trajectory is created, the screen is refreshed. Therefore, the user may wait to see if the straight moving trajectory changes into a smooth curve.
In the simultaneous line-interpolation, the sampled circles or points are connected by the tangent lines to constitute the quadrangles, with the result that angled portions 400 and 401 (FIG. 2) may occur. Therefore, the moving trajectory of the touch unit is not created as a fully smooth curve.
In the conventional technology, a user may suffer inconvenience of use (post-processing smoothing) so as to obtain a smooth curved trajectory, or smoothing may be damaged so as to ensure convenience of use (simultaneous line-interpolation).